A method is disclosed for making palatable methionine-restricted foods, to deliver a methionine-restricted diet to human or veterinary patients. A protein or a food product containing protein is partially oxidized, preferably with ozone, to oxidize nearly all of the methionine and cysteine. After oxidation, tryptophan and lysine are optionally added back since they tend to be oxidized also. Optionally, a small amount of methionine is also added back so that the final methionine is within a preferred range of about 0.85 to about 1.8 gram methionine per 100 gram total protein, preferably about 1.2 gram per 100 gram total protein.